Venetian blinds allow the effective control of the light admitted through a window. By adjusting the tilt orientation of the assembly of parallel blind slats sunlight glare may be blocked while still allowing sunlight or daylight to enter the room. Rotating the slab to a near vertical orientation permits the window opening to be fully obscured. Because the orientation of the slab required to achieve a desired lighting effect will vary with the time of day and the position of the sun, venetian blinds are provided with manual tilt control mechanisms which allow the quick adjustment of slat orientation.
The horizontal slab are suspended by two or more ladders formed of fabric tape or cords. Each ladder has two vertically extending legs which extend in front and in back of the slats, with flexible rungs which extend between the legs to engage the slats. The ladder legs extend into a headrail above the slats and are typically connected to a rotatable tilt drum or round tilt tube such that rotation of the drum or tube causes one ladder leg to be taken up on the drum while the other is played out from the drum or tube. The coordinated shortening of one ladder leg while the other is lengthened causes the slats, which are connected between the legs, to tilt about an axis roughly extending through the center of each slat.
Because the slats are supported on two or more ladders, it is essential that all ladders be adjusted simultaneously and to the same degree. Joint adjustment of the multiple ladders is typically achieved by a single rigid tilt rod which extends through and is fixed to both tilt drums, or by one unified tilt tube. A mechanical linkage extends from the tilt rod to a tilt actuator control, typically a knob or crank. By turning the actuator a user may set the desired degree of blind tilt.
In institutional installations where children or non-responsible persons may have access to the blind tilt controls, narrow slatted blinds are often used between panes of glass and behind window screens which are connected to the tilt rod or tube in an arrangement that allows the ladder legs to slip on the drums or tube if the tilt actuator is advanced too far. To achieve this tilt arrangement, the two legs of the ladder are typically joined in the head rail by a metal sleeve which is crimped over the separate ends of each leg to form a single loop. The plastic legs are then heat-welded together. The connected legs are looped about the drum or tube with one leg descending behind the tube and one in front. With this arrangement continued actuation of the tilt actuator after the blinds have taken on their maximum tilt in one direction will result in the harmless slipping of the looped legs on the tilt drum or tube.
The possibility exists, however, that the looped legs held on the tilt drum or tube may overlap, with one loop being elevated by an underlying loop. Particularly if the increased thickness of the sleeve is overlapped, the total length of the ladders which extend from the headrail will be reduced, with the result that all the supported slats will be raised. As the overlapping of the loops is only occasional, it is likely that one ladder may be shortened while the other remains at full length. Such a disparity will cause the entire assembly of slats to tilt sidewardly, causing an unattractive distortion to the blind appearance.
What is needed is a tilt mechanism which prevents overwinding of the ladders, yet which prevents the overlapping of the looped ladder legs.
Complete venetian blind assemblies are often supplied by the blind manufacturer to be installed in windows manufactured elsewhere. If a blind is mounted on the interior of a window the tilt rod is usually controlled by an actuator rod which hangs freely from a gearing mechanism which converts the rotation of the actuator rod about a generally vertical axis to the horizontal rotation of the tilt rod. However, blinds may be installed between a casement window and a screen, or between the two glass panes of a double pane window. In such installations the blinds are not directly accessible from the window interior. A system of flexible cables or gear boxes and rods has typically been employed to permit the tilt rod to be adjusted by the rotation of a control handle or knob which extends from the window frame interior. In conventional assemblies, one or more flexible cables permit the rotary motion of the control handle to turn comers as needed. The flexible cables are in turn connected to a rigid vertically extending rod by tiny set screws which lock a cable firing to the rigid rod. Installation of this type of cable system can present problems. The set screws required to connect the rod to the cable are extremely small and hence difficult to manipulate and require ultra-small wrenches and tools. Furthermore, because the cable and rods are unguided, the lengths of the cables and rods must be precisely matched to the size of the window opening in which they are installed. This precise length and capture of the rod by set screws is the only means of guiding the assembly. The cables and rod are under tension throughout and are thereby held in position. In addition, after installation them remains the possibility that vibration or other disturbance will cause the set screws to work loose, thereby disabling the linkage.
What is needed is a mechanical linkage between the rotating actuator handle and the tilt rod which is simple to install, has greater dimensional tolerances, and which is durable.